U.S. patent number 7,723,610 [Application Number 12/406,760] was granted by the patent office on 2010-05-25 for titanium oxide-based sol-gel polymer.
This patent grant is currently assigned to Centre National de la Recherche Scientifique (C.N.R.S.). Invention is credited to Luc Brohan, Maria Teresa Caldes-Rouillon, Olivier Joubert, Yves Piffard, Eric Puzenat, Annabelle Rouet, Hari Sutrisno.
United States Patent |
7,723,610 |
Brohan , et al. |
May 25, 2010 |
Titanium oxide-based sol-gel polymer
Abstract
The invention relates to a titanium oxide-based polymer
composition. The inventive composition comprises a
TiO.sub.x(OH).sub.y(H.sub.2O).sub.z(x+y-+z=3) titanium oxide-based
polymer in the form of a gel or sol. Said polymer, which has a
one-dimensional (1D) structure, is made from concentrically-wound
fibers having a periodicity which is deduced from the spacing
between said fibers, of between 3.5 .ANG. and 4 .ANG.. Each fiber
comprises TiO.sub.6octahedrons and each TiO.sub.6octahedron shares
two opposite edges with two adjacent octahedrons (2.times.2.92
.ANG.) in order to form infinite chains which develop along the
axis of a fiber. According to the invention, two adjacent chains
form double lines as a result of the shared edges (2.times.3.27
.ANG.). The inventive polymer is suitable for use as a
photosensitive element in a photovoltaic cell, such as a sunscreen
for a window.
Inventors: |
Brohan; Luc (La
Chapelle-sur-Erdre, FR), Sutrisno; Hari (Tulungagung,
ID), Piffard; Yves (La Chapelle-sur-Erdre,
FR), Caldes-Rouillon; Maria Teresa (Nantes,
FR), Joubert; Olivier (Brains, FR),
Puzenat; Eric (Nantes, FR), Rouet; Annabelle
(Nantes, FR) |
Assignee: |
Centre National de la Recherche
Scientifique (C.N.R.S.) (Paris, FR)
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Family
ID: |
27619725 |
Appl.
No.: |
12/406,760 |
Filed: |
March 18, 2009 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20090173383 A1 |
Jul 9, 2009 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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10502399 |
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7524482 |
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PCT/FR03/00106 |
Jan 14, 2003 |
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Foreign Application Priority Data
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Jan 29, 2002 [FR] |
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02 01055 |
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Current U.S.
Class: |
136/263;
501/95.2; 429/111; 423/608; 252/520.22; 136/252 |
Current CPC
Class: |
B82Y
30/00 (20130101); C01G 23/0536 (20130101); C01P
2004/64 (20130101); C01P 2002/76 (20130101); C01P
2004/10 (20130101); C01P 2006/60 (20130101) |
Current International
Class: |
C01G
25/02 (20060101); C01G 27/02 (20060101); C04B
35/00 (20060101); H01B 1/02 (20060101); H01L
35/00 (20060101); H01M 6/30 (20060101) |
Field of
Search: |
;423/579,592.1,608-616
;501/95.2 ;136/252-265 ;429/111,44 ;252/520.22 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
Caruso et al., "Titanium Dioxide Tubes from Sol-Gel Coating of
Electrospun Polymer Fibers", Adv. Mater. 2001, 13, No. 20,
1577-1579. cited by examiner .
Kallala et al. "Structures of inorganic polymers in sol-gel
processes based on titanium oxide", Physical Review E 44 (5), Nov.
1993, 48-. cited by examiner .
Z. Wang et al., Functional and Smart Materials--Structural
Evolution and Structure Analysis, 1998, pp. 77-78, Plenum Press,
NY. cited by other .
Yang et al., "Study of stability of sol-gel solutions," Journal of
Guilin University of Technology, 1999, pp. 371-374, vol. 19(4),
Chemical Abstracts database accession No. 132:199483 XP002216420.
cited by other .
Zheng et al., "Studies on preparation and properties of Ti02/PVP
nano-composites by sol-gel method," Jinshu Xuebao, 1999, pp.
1224-1228, vol. 35(11), Chemical Abstracts database accession No.
132:140878 XP002216421. cited by other .
Fu et al., "Preparation of monolithic TiO2 gel in presence of
N,N-dimethylformamide," Gongneng Cailiao, 2001, pp. 319-320, vol.
32(3), Chemical Abstracts accession No. 135:347833 XP002216419.
cited by other.
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Primary Examiner: Bos; Steven
Assistant Examiner: Zimmer; Anthony J
Attorney, Agent or Firm: Buchanan Ingersoll & Rooney
PC
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATION
The present application is a division of U.S. patent application
Ser. No. 10/502,399 filed Mar. 25, 2005, which is a national stage
filing of International Patent Application No. PCT/FR2003/00106
filed Jan. 14, 2003, which claims the priority of French Patent
Application No. 02/01055 filed Jan. 29, 2002, the entire contents
of which are incorporated herein by reference, the entire contents
of which are incorporated herein by reference.
Claims
The invention claimed is:
1. A polymer composition essentially formed by a polymer based on
titanium oxide, which is represented by the formula
TiO.sub.x(OH).sub.y(H.sub.2O).sub.z in which x+y+z=3, in the form
of a gel or in the form of a sol, wherein: the polymer comprises
fibers wound concentrically with a periodicity, deduced from the
space in between the fibers, of between 3.5 .ANG. and 4 .ANG.; each
fiber is made up of TiO.sub.6 octahedra; each TiO.sub.6 octahedron
shares two opposed edges with two adjacent octahedra in order to
form chains that grow along the axis of a fiber; two adjacent
chains form double strands by the communing of edges; and the
polymer composition comprises dimethylammonium chloride (DMAC1) and
formic acid.
2. The polymer composition of claim 1, wherein the polymer
composition is translucent and contains titanium in oxidized form
Ti.sup.4+.
3. The polymer composition of claim 1, wherein the polymer
composition has a violet, blue or green coloration and at least
part of the titanium of the polymer is in Ti.sup.3+ form.
4. A photovoltaic cell comprising a photoanode and a photocathode
in an electrolyte, wherein: the photoanode comprises a conductive
glass plate coated with a layer of the polymer composition of claim
1 in gel form, containing titanium in Ti.sup.3+ form; and the
photocathode comprises a conductive glass plate coated with a layer
of the polymer composition of claim 1 in gel form containing
titanium in Ti.sup.4+ form.
5. Solar protection glazing, wherein the solar protection glazing
comprises a glass plate covered with a layer of the polymer
composition of claim 1 in the form of a gel.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a polymer composition based on
titanium oxide, to its use as a semiconductor element in a
photovoltaic cell, and to a method for preparing it.
2. Description of the Related Art
Photovoltaic cells convert solar energy into electricity by
exploiting the photovoltaic effect that exists at the interface of
a p-n junction between two semiconductors. Semiconductors based on
silicon have been used, but the high cost of the raw material is
not favorable to the industrial development of such cells. Silicon
has therefore been replaced with titanium oxide TiO.sub.2 which is
an inexpensive semiconductor and has stable photocatalytic
properties. Its applications in the photovoltaic field are,
however, limited, as it absorbs only within a narrow range of the
solar spectrum, owing to a wide bandgap. This range corresponds to
the UV part and covers less than 10% of the entire solar spectrum.
One solution consists in covering the surface of the titanium oxide
with a photosensitizer in order to extend its photoactivity range
into the region of the solar spectrum. This technique has been
employed using a ruthenium polypyridinic complex as photosensitizer
(U.S. Pat. No. 5,084,365) and it has allowed efficiencies of around
12% to be achieved. The cells containing, as semiconductor,
titanium oxide activated by a photosensitizer have a production
cost less than that of the photovoltaic cells of the prior art.
However, their operating lifetime, which is about 10 years, is
considerably shorter than that of single-crystal silicon cells
(which is around 20 years), and their efficiency is lower.
SUMMARY OF THE INVENTION
The inventors have now found that the performance of a titanium
oxide used as semiconductor in a photovoltaic cell can be optimized
by controlling the microstructural or mesostructural scale of the
morphology. The object of the present invention is therefore to
provide a particular titanium oxide exhibiting improved performance
when it is used as semiconductor element in a photovoltaic
cell.
The subject of the present invention is therefore a composition
based on titanium oxide, a method for preparing it and a
photovoltaic cell that contains it as semiconductor element.
BRIEF DESCRIPTION OF THE FIGURES OF THE DRAWINGS
FIG. 1 shows the optical absorption spectrum of the untreated
fraction of solutions 1 to 4;
FIG. 2 shows the optical absorption spectrum of the fraction of
each of solutions 1 to 4 subjected to UV irradiation for 180
hours;
FIG. 3 shows the optical absorption spectrum of the fraction of
solutions 1 to 4 subjected to heating at 65.degree. C. for 15
hours;
FIG. 4 shows the optical absorption spectrum of the fraction of
solutions 1 to 4 subjected to heating at 65.degree. C. for 15 hours
followed by UV irradiation for 15 hours;
FIG. 5 shows the idealized structure of a TiO(OH).sub.2 polymer
ribbon;
FIG. 6 shows an absorption spectrum for a specimen using a Cary
UV-Vis-NR absorption spectrometer; and
FIG. 7 shows an absorption spectrum for a specimen using a Cary
UV-Vis-NR absorption spectrometer.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The composition according to the present invention is essentially
formed by a polymer based on titanium oxide, which may be
represented by the formula TiO.sub.x(OH).sub.y(H.sub.2O).sub.z in
which x+y+z=3, in the form of a gel or in the form of a sol. It is
characterized in that:
the polymer has a structure of one-dimensional (1D) character and
it consists of fibers wound concentrically with a periodicity,
deduced from the space in between the fibers, of between 3.5 .ANG.
and 4 .ANG.;
each fiber is made up of TiO.sub.6 octahedra;
each TiO.sub.6 octahedron shares two opposed edges with two
adjacent octahedra (2.times.2.92 .ANG.) in order to form infinite
chains that grow along the axis of a fiber; and
two adjacent chains form double strands by the commoning of edges
(2.times.3.27 .ANG.).
The one-dimensional structure of the
TiO.sub.x(OH).sub.y(H.sub.2O).sub.z polymer (denoted hereafter by
TiO polymer) is detected by transmission electron microscopy. The
chain structure is revealed by EXAFS analysis (Extended X-ray
Absorption Fine Structure).
A polymer composition according to the invention (denoted hereafter
by polymer TiO composition) may be translucent or be colored. The
composition is translucent when it is shielded from the light and
when the titanium is essentially in the Ti.sup.4+ form, the polymer
then corresponding to the formula TiO(OH).sub.2. When the titanium
is essentially in the Ti.sup.3+ form in the TiO polymer, a broad
absorption band exists in the visible range (between 400 and 850
nm), which results in a violet, blue, midnight blue or green
coloration of the composition. The coloration changes with the
proportion of Ti.sup.3+. It goes from green, in the case of low
Ti.sup.3+ concentrations to blue in the case of high
concentrations. When all the titanium is in the Ti.sup.3+ form, the
TiO polymer corresponds to the formula TiO(OH)(H.sub.2O).
A TiO polymer composition according to the invention may be
obtained from TiOCl.sub.2. Since the TiOCl.sub.2 compound is highly
hydroscopic, it is used in the TiOCl.sub.2.yHCl form, i.e. in
solution, dissolved in concentrated hydrochloric acid.
Advantageously, the concentrated HCL solution is an approximately
2M aqueous solution. The TiOCl.sub.2 concentration in this solution
is preferably between 4M and 5M.
According to a first embodiment, the TiO polymer composition
according to the invention may be obtained in oxidized form, in
which the titanium is in the Ti.sup.4+ oxidation state, by a method
that consists in:
preparing a TiOCl.sub.2 solution in dimethylformamide (DMF) by
introducing TiOCl.sub.2.yHCl into DMF, in proportions such that the
concentration (C.sub.Ti) of Ti atoms is less than 2M;
heating the solution thus obtained to a temperature between room
temperature and 90.degree. C.; and
holding the solution at this temperature for a certain time.
The temperature hold time depends on the temperature. For example,
when the solution is held at 65.degree. C., a time of 24 h is
sufficient.
The TiO(OH).sub.2 polymer thus obtained may be converted into its
reduced form in which at least part of the titanium is in the
Ti.sup.3+ oxidation state, by UV irradiation (for example at
.lamda.=360 nm) of the composition in an inert atmosphere, which
induces a coloration (violet, blue or green, depending on the
Ti.sup.3+ concentration), this coloration being maintained when the
irradiation ceases.
The TiO polymer composition is obtained in the form of a colloidal
solution or sol in DMF when C.sub.Ti is less than 1M and in the
form of a gel when C.sub.Ti is greater than 1M.
In a second embodiment, the TiO polymer composition of the
invention is obtained directly in reduced form, in which at least a
part of the titanium is in the Ti.sup.3+ oxidation state by a
method consisting in reducing TiOCl.sub.2 using a species that is
oxidizable at a potential of less than -0.05 V with respect to a
standard hydrogen electrode. As an example, mention may be made of
metals in oxidation state zero, such as Ni, Fe, Al, Cr, Zr, Ti, Nb,
Cs, Rb, Na, K, Li, La and Ce, ionic compounds, in which the cation
is chosen from V.sup.2+, Ti.sup.2+ and Cr.sup.2+, and ionic
compounds in which the anion is chosen from S.sub.2O.sub.3.sup.2-,
H.sup.-, and S.sub.2.sup.2-. Zinc is particularly preferred. In
this case, the TiO polymer composition according to the invention
is obtained with a coloration. If it is then irradiated by UV
radiation, the content of Ti.sup.3+ species increases and its
coloration changes from green to violet and then to blue as the
content of Ti.sup.3+ ions increases.
A first variant of the method of preparation involving reduction by
an oxidizable species, consists in preparing a TiOCl.sub.2 solution
in dimethylformamide (DMF) starting with TiOCl.sub.2.yHCl, such
that the concentration (C.sub.Ti) of Ti atoms is less than 2M, in
adding the oxidizable species, in heating the solution to a
temperature between room temperature and 90.degree. C. and in
holding the solution at this temperature for a certain time, which
depends on the temperature.
A second variant of the method of preparation, involving reduction
by an oxidizable species, consists in introducing the oxidizable
species into a TiOCl.sub.2.yHCl solution in which C.sub.Ti is less
than 2M, and in maintaining the reaction mixture at a temperature
between room temperature and 90.degree. C.
In both variants, it is preferred to introduce the metal in the
form of chips. The ionic compound may be introduced in the form of
powder, liquid or gas.
When a composition according to the invention is prepared by a
method using DMF, it contains dimethylammonium chloride and formic
acid. These constituents may be detected for example by proton
(.sup.1H) NMR analysis, which also makes it possible to determine
the quantity thereof. When the C.sub.Ti concentration in the
initial reaction mixture is less than 1M, the composition is a
colloidal solution of uncrosslinked polymer in DMF. When the
initial concentration C.sub.Ti is greater than 1M, the polymer is
crosslinked and the composition is in gel form.
When a composition according to the invention is prepared according
to the second variant of the method involving reduction by an
oxidizable species, i.e. in the absence of DMF, said composition is
a colloidal solution of uncrosslinked polymer in water when
C.sub.Ti is less than 1M. When C.sub.Ti is greater than 1M, the
polymer is crosslinked and the composition is in gel form.
Whatever the method used to obtain the reduced form of the polymer
exhibiting coloration, the oxidized form may be obtained by
subjecting the polymer composition to oxidation in air so that it
resumes its translucent appearance.
A TiO polymer composition according to the invention is
photochromic in character. When it is obtained in gel form, it may
advantageously be used in a photovoltaic cell in which the active
material of the photoanode is the composition containing the
Ti.sup.3+ reduced form, and the active material of the photocathode
is a composition containing the Ti.sup.4+ oxidized form.
A composition of the invention may furthermore be used for the
production of solar protection glazing. A glass pane covered with a
composition of the invention in the form of a gel remains
translucent when it is away from sunlight. Under the effect of
irradiation by visible light, the glass pane assumes a midnight
blue coloration. This phenomenon can be made reversible by applying
a potential allowing oxidation.
The present invention will be described in greater detail by the
following examples, which are given for illustration, but the
invention is not, however, limited thereto.
EXAMPLE 1
10 ml of DMF at 4 ml of a 4.3M TiOCl.sub.2 solution in 2M
hydrochloric acid were introduced into a test tube, under an inert
atmosphere of N.sub.2. After having closed the tube, it was placed
in an oven at 65.degree. C. and maintained at this temperature for
24 hours. It was then left to cool down and the appearance of a
transparent gel was observed at room temperature.
The presence of dimethylammonium chloride and formic acid was
detected by .sup.1H and .sup.13C NMR by IR and by Raman.
After having been exposed to visible light, the gel had an intense
blue coloration, as a result of the reduction of Ti.sup.4+ to
Ti.sup.3+. This phenomenon is reversible, and by opening the tube
an oxidation takes place in the presence of the oxygen from the
air, the gel again becoming transparent after a few minutes.
High-resolution imaging, obtained by transmission electron
microscopy, showed that the structure of the TiO(OH).sub.2 polymer
obtained was of 1-dimensional (1D) character. The fibers of the
polymer were wound concentrically in the manner of a cotton bol.
The presence of substantial disorder in the direction perpendicular
to the stack of fibers was manifested in the diffraction pattern by
the presence of diffuse lenticular spots. The periodicity, deduced
from the spacing between the fibers, was estimated to be 3.5-4
.ANG..
EXAMPLE 2
The operating method described in example 1 was repeated, for
several preparations, varying only the concentration C.sub.Ti in
the test tube. Each test tube, filled with air or N.sub.2 was
subjected to a heat treatment similar to that of example 1.
The formation of a gel was observed only for C.sub.Ti
concentrations between 1M and 2M. For concentrations where
C.sub.Ti<1M, the mixture remained liquid and consisted of a
colloidal solution of the polymer. For concentrations where
C.sub.Ti>2M, an opaque white product forms that contains a
transparent polymeric phase and an amorphous white precipitate, or
a white precipitate of anatase in the case of very high
concentrations.
EXAMPLE 3
The optical properties of various specimens were measured for
various irradiation states. For this purpose, four specimens were
prepared, in air or in nitrogen, from a TiOCl.sub.2 solution
identical to that used in example 1:
TABLE-US-00001 No. C.sub.Ti (mol/l) Vol. of TiOC1.sub.2 Vol. of DMF
O.sub.2 N.sub.2 1 1.6M 1.3 ml 2.15 ml X 2 1.6M 1.3 ml 2.15 ml X 3
1.45M 1.1 ml 2.15 ml X 4 1.45M 1.1 ml 2.15 ml X
In a first series of tests, a fraction of each of solutions 1 to 4
was subjected to UV irradiation (.lamda.=360 nm) for 180 hours.
In a second series of tests, a fraction of each of solutions 1 to 4
was subjected to a heat treatment at 65.degree. C. for 15 hours,
after which each fraction was subjected to UV irradiation
(.lamda.=360 nm) for 180 hours.
FIGS. 1 to 4 show the optical absorption spectra of the solutions
after various treatments. The absorption A, in arbitrary units, is
plotted on the Y-axis. The wavelength .lamda., in nanometers, is
plotted on the X-axis. In each of the figures, the solution spectra
are indicated by the following symbols:
TABLE-US-00002 Solution 1 Solution 2 Solution 3 Solution 4
.circle-solid. .tangle-solidup. .smallcircle. .DELTA.
FIG. 1 shows the optical absorption spectrum of the untreated
fraction of each of solutions 1 to 4. The four spectra are almost
identical and show that there is no absorption in the visible range
and that the influence of both the concentration and the
conditioning atmosphere is negligible.
FIG. 2 shows the optical absorption spectrum of the fraction of
each of solutions 1 to 4 subjected to UV irradiation for 180 hours.
The spectra indicate the presence of a strong absorption, which
extends over a wide range in the visible, and also a slight shift
of the absorption edge toward shorter wavelengths.
FIG. 3 shows the optical absorption spectrum of the fraction of
each of solutions 1 to 4 subjected to heating at 65.degree. C. for
15 hours. The spectra indicate a slight shift of the absorption
edge toward shorter wavelengths relative to the spectra of the
initial, untreated solutions.
FIG. 4 shows the optical absorption spectrum of the fraction of
each of solutions 1 to 4 subjected to heating at 65.degree. C. for
15 hours followed by UV irradiation for 15 hours. The spectra
indicate a broad absorption band in the visible range. The
absorption is greater in the case of the gel and its maximum is
shifted toward longer wavelengths than in the case of the
corresponding initial solutions.
The structure of the TiO(OH).sub.2 polymer gel was characterized by
titanium K-edge EXAFS analysis. The results of the fine structure
analysis give the number N of neighboring atoms, the distance R
between an absorbent atom and its neighbors, the Debye-Waller
factor sigma., the energy shift .DELTA.E.sub.o and the residue
.rho.. The results are given in the table below.
TABLE-US-00003 TiO(OH).sub.2 N R (.ANG.) .SIGMA. .times. 10.sup.2
(.ANG.) .DELTA.E.sub.O (eV) P (%) Ti--O 3.91 1.89 1.3 0.48 Ti--O
2.08 1.98 2.8 0.00 2.32 Ti--Ti 2.28 2.92 6.3 2.84 Ti--Ti 1.71 3.27
1.7 6.85
The idealized structure of the TiO(OH).sub.2 polymer ribbon, which
has a 1D character, is shown in FIG. 5(B). It is similar to the
structure observed in the case of hollandite. Each TiO.sub.6
octahedron shares two opposed edges with two adjacent octahedra
(2.92 .ANG.) in order to form infinite chains that run along the
axis of the fiber. Two adjacent chains form double strands by
commoning edges (2.times.3.27 .ANG.). Because of the difference
between the actual number of neighbors and the ideal value of 2,
the polymer obtained may be crosslinked, as shown in FIG. 5(A).
EXAMPLE 4
Four starting solutions were prepared by introducing a TiOCl.sub.2
solution in concentrated HCl into DMF, in an amount such that the
C.sub.Ti concentrations were 0.03M, 0.04M, 0.05M and 0.06M
respectively. 100 mg of zinc chips were added to 3 ml of each of
these solutions.
The change in coloration was monitored over time by measuring the
absorption of the specimens using a Cary UV-Vis-NIR absorption
spectrometer between 300 and 1200 nm. The absorption spectra are
shown in FIGS. 6 and 7. The absorption Abs. is plotted on the
Y-axis (in arbitrary units). The wavelength .lamda. is plotted on
the X-axis (in nm). The spectra show that, between t=0 min and
t=500 min (FIG. 6), an absorption peak is formed at 550 nm, which
increases over time and is accompanied by three shoulders, at 630
nm, at 740 nm and at about 900 nm. After 500 min (FIG. 7), this
peak tends to disappear and leaves instead a broad absorption band
lying between 630 and 740 nm. After 3150 min, i.e. more than 2
days, there is substantial absorption whatever the wavelength in
the visible range. However, two peaks appear at 550 nm and 710
nm.
* * * * *